linux-ext4 - Re: [PATCH 2/2] ext4, dax: set ext4_dax

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Date:   Tue, 11 Sep 2018 11:15:18 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Toshi Kani <toshi.kani@....com>
Cc:     Jan Kara <jack@...e.cz>, "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4, dax: set ext4_dax_aops for dax files

On Tue, Sep 11, 2018 at 8:42 AM, Toshi Kani <toshi.kani@....com> wrote:
> Sync syscall to an existing DAX file needs to flush processor cache,
> but it does not currently.  This is because 'ext4_da_aops' is set to
> address_space_operations of existing DAX files, instead of 'ext4_dax_aops',
> since S_DAX flag is set after ext4_set_aops() in the open path.
>
>   New file
>   --------
>   lookup_open
>     ext4_create
>       __ext4_new_inode
>         ext4_set_inode_flags   // Set S_DAX flag
>       ext4_set_aops            // Set aops to ext4_dax_aops
>
>   Existing file
>   -------------
>   lookup_open
>     ext4_lookup
>       ext4_iget
>         ext4_set_aops          // Set aops to ext4_da_aops
>         ext4_set_inode_flags   // Set S_DAX flag
>
> Change ext4_iget() to call ext4_set_inode_flags() before ext4_set_aops().
>
> Fixes: 5f0663bb4a64f588f0a2dd6d1be68d40f9af0086

Same format nit:

Fixes: 5f0663bb4a64 ("ext4, dax: introduce ext4_dax_aops")
Cc: <stable@...r.kernel.org>


> Signed-off-by: Toshi Kani <toshi.kani@....com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> ---
>  fs/ext4/inode.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 775cd9b4af55..93cbbb859c40 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4998,6 +4998,8 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
>         if (ret)
>                 goto bad_inode;
>
> +       ext4_set_inode_flags(inode);
> +

Hmm, does this have unintended behavior changes?

I notice that there are some checks for flags "IS_APPEND(inode) ||
IS_IMMUTABLE(inode)" *before* the call to ext4_set_inode_flags(). I
didn't look too much deeper at whether those checks are bogus, but it
would seem safer to do something like this for a lower risk fix.

Thoughts?

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d0dd585add6a..1e9ab445c777 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4999,7 +4999,6 @@ struct inode *ext4_iget(struct super_block *sb,
unsigned long ino)
        if (S_ISREG(inode->i_mode)) {
                inode->i_op = &ext4_file_inode_operations;
                inode->i_fop = &ext4_file_operations;
-               ext4_set_aops(inode);
        } else if (S_ISDIR(inode->i_mode)) {
                inode->i_op = &ext4_dir_inode_operations;
                inode->i_fop = &ext4_dir_operations;
@@ -5042,6 +5041,12 @@ struct inode *ext4_iget(struct super_block *sb,
unsigned long ino)
        }
        brelse(iloc.bh);
        ext4_set_inode_flags(inode);
+       /*
+        * Now that we have determined whether DAX is enabled, set the
+        * proper address spaces operations
+        */
+       if (S_ISREG(inode->i_mode))
+               ext4_set_aops(inode);

        unlock_new_inode(inode);
        return inode;